The role of connective tissue growth factor in pulmonary fibrosis induced by paraquat

Objective To examine the role of connective tissue growth factor (CTGF) in a rat model of paraquat (PQ)-induced pulmonary fibrosis. Methods In the laboratory of Medical School of Nanjing University, 48 adult male Sprague-Dawley (SD) rats were randomly(random number) divided into two groups. The experimental group received a single intraperitoneal injection of PQ (30 mg/kg), while the control group received an equivalent volume of sterile saline. The rats were then sacrificed and the left lungs were collected on 7th, 14th and 28th day, respectively. HE staining, Masson staining and hydroxyproline content analysis were used to determine the quantity of collagen, and the fibrosis process and severity were evaluated. Western blotting and immunohistochemical staining was used to detect the expression of CTGF. MRC-5 human lung fibroblasts were exposed to different concentrations of PQ (50-500 µmol/L) for 3 days. The proliferation, migration and differentiation of MRC-5 cells were investigated by CCK8, Transwell and Western blotting after exposing with various concentrations of CTGF (50-200 ng/mL). Data was analyzed with SPSS18.0. Results At 2 weeks after PQ administration, lung tissue sections exhibited a marked thickening of the alveolar walls with an accumulation of interstitial cells with a fibroblastic appearance. Masson staining revealed a patchy distribution of collagen deposition, indicating pulmonary fibrogenesis. Western-blott and immunohistochemical staining demonstrated that CTGF expression was significantly upregulated in the PQ-treated group (P<0.01). Similarly, CTGF expression in PQ-treated MRC-5 cells was increased in a dose-dependent manner (P<0.01). In addition, CTGF promoted the proliferation and migration of MRC-5 cells (P<0.01), and induced the differentiation of fibroblasts into myofibroblasts. Conclusions These findings demonstrate that PQ can increase CTGF expression, which may be important in PQ-induced pulmonary fibrogenesis. Therefore, this growth factor can be considered as a potential pharmacological target. Key words: Paraquat; Pulmonary fibrosis; Connective tissue growth factor; Myofibroblast differentiation; Therapeutic target